At present, there are many types of acoustical transducer or loudspeaker arrangements designed to accurately reproduce sounds in high-fidelity sound systems. The most familiar type of such transducers is the well-known cone speaker which produces sound energy by vibrating a cone-shaped transducer element by means of an electromagnetic voice-coil arrangement. Various modifications of this arrangement have been developed including acoustic suspension speakers, motional feedback speakers and other arrangements to reduce distortion and improve fidelity of the reproduced sound.
One of the major disadvantages with cone speakers is that, due to their physical construction, they must be driven over a narrow ring-shaped area. This type of drive induces unwanted structural vibrations in the cone and causes distortion. In addition, most cone speakers have limited dispersion. That is, the sound quality perceived by a listener located in a room with such a speaker changes when the listener moves about the room. In order to increase the dispersion of a cone speaker it is necessary to make the physical size of the speaker cone as small as possible so that the speaker acts as a "point" source. Unfortunately, small speakers have limited power handling capability.
Loudspeakers employing metallic ribbons and plastic or paper diaphragms to reproduce sounds are also well-known in the art and have been demonstrated to have advantages compared to the cone speakers. In particular, such speakers may have better dispersion characteristics than the cone speakers for a given power handling capability because they approximate a "line" source rather than a "point" source. Unfortunately, due to the mechanical characteristics of the metallic ribbons and non-metallic panels and unfortunate acoustical design, such speakers often have mechanical resonances or other distortions which prevent the speakers from producing an accurate reproduction of the sound with high resolution over the full acoustic frequency range normally encountered during high-fidelity sound reproduction. For example, such speakers are often subject to a phenomenon known as "diffraction" which occurs when, due to poor speaker design, the speaker acts as a multiple line source instead of a single line source. In addition, the non-metallic materials used to fabricate panel speakers were subject to deterioration with age due to stretching of the speaker materials.
In order to achieve good frequency response, especially in mid-range frequencies, it has been found necessary to use a long, narrow lightweight ribbon. Prior art ribbon midrange tweeter designs have been unable to properly align such a ribbon with the speaker's magnetic field and to keep the ribbon centered within its supporting frame for relatively high power levels. Previous prior art ribbon designs have not demonstrated the capability to reproduce music at lifelike sound power levels.
In addition, prior art midrange ribbon transducer designs have not been able to minimize the acoustical leakage around the sides of the ribbon or provide for the proper electrical and dynamic characteristics of the acoustical ribbon element.
Further, prior art ribbon systems have often utilized classical cone-type woofers instead of ribbon woofer elements due to problems encountered in the design of large area ribbons necessary for good low-frequency response. The cone-type woofers were subject to the distortion and dispersion problems set forth in detail above.
Therefore, it is an object of the present invention to provide a speaker system which provides accurate, high-resolution reproduction of sound over the full acoustic frequency range normally encountered in sound reproduction systems.
It is a further object of the present invention to produce a speaker system with excellent dispersion over the full acoustic frequency range.
It is yet a further object of the invention to produce a ribbon speaker system which is easily constructed from readily available materials.
It is yet another object of the invention to produce a ribbon speaker system which eliminates the mechanical resonances and distortions typically found in prior art cone, planar and ribbon speakers.
It is yet a further object of the present invention to provide a speaker system in which the transducers are not subject to deterioration with age.
It is still another object of the invention to provide a speaker system with means for automatic centering of the speaker ribbons within their supporting framework.
It is still another object of the invention to provide a speaker system with a wide bandwidth frequency response.
It is yet another object of the invention to provide a tweeter transducer which acts like a theoretical "line source".
It is a further object of the invention to provide a line source tweeter transducer which utilizes only a single common magnetic structure and no back wave damping materials.